A typical prior art head and disk system 10 is illustrated in FIG. 1. In operation the magnetic transducer 20 is supported by the suspension 13 as it flies above the disk 16. The magnetic transducer 20, usually called a “head” or “slider,” is composed of elements that perform the task of writing magnetic transitions (the write head 23) and reading the magnetic transitions (the read head 12). The electrical signals to and from the read and write heads 12, 23 travel along conductive paths (leads) 14 which are attached to or embedded in the suspension 13. The magnetic transducer 20 is positioned over points at varying radial distances from the center of the disk 16 to read and write circular tracks (not shown). The disk 16 is attached to a spindle 18 that is driven by a spindle motor 24 to rotate the disk 16. The disk 16 comprises a substrate 26 on which a plurality of thin films 21 are deposited. The thin films 21 include ferromagnetic material in which the write head 23 records the magnetic transitions in which information is encoded.
Reference is made to FIG. 2 to illustrate the thin film layers in a particular embodiment of a magnetic film disk 16. The substrate 26 is glass. An amorphous initial thin film deposited on the substrate will be called a pre-seed layer 31. The seed layer 32 is deposited onto the pre-seed layer. Typically both the pre-seed layer and seed layer are relatively thin layers. Materials proposed for use as seed layers include chromium, titanium, tantalum, Ni3P, MgO, carbon, tungsten, AlN, FeAl, NiAl and RuAl. In U.S. Pat. No. 5,789,056 to Bian, et al., the use of a CrTi seed layer is described. Following the seed layer is typically a chromium or chromium alloy underlayer 33 such as Cr, CrV and CrTi. The ferromagnetic layer 34 in the thin films is based on various alloys of cobalt, nickel and iron. For example, a commonly used alloy is CoPtCr. Additional elements such as tantalum and boron are often used in the magnetic alloy. A protective overcoat layer is used to improve wearability and corrosion resistance. The disk embodiment described above is one of many possibilities. For example, multiple seed layers, multiple underlayers and multiple magnetic layers have all been proposed in the prior art.
The preferred orientation (PO) of the various crystalline materials forming the layers on the disk, as discussed herein, is not necessarily an exclusive orientation which may be found in the material, but is merely the most prominent orientation. When the Cr underlayer is sputter deposited at a sufficiently elevated temperature on a NiP-coated AlMg substrate a [200] PO is usually formed. This PO promotes the epitaxial growth of [11-20] PO of the hexagonal close-packed (hcp) cobalt (Co) alloy, and thereby improves the magnetic performance of the disk. The [11-20] PO refers to a film of hexagonal structure whose (11-20) planes are predominantly parallel to the surface of the film. Likewise the [10-10] PO refers to a film of hexagonal structure whose (10-10) planes are predominantly parallel to the surface of the film. The [10-10] PO can be epitaxially grown on an appropriate underlayer with a PO of [112].
One technique used in the prior art to improve magnetic recording performance on thin film disks is circumferential polishing to create a pattern of fine “scratches” (circumferential texture) which are generally oriented along tracks (concentric circles) on the disk surface. The scale of the texture of commercial thin film disks is microscopic with a peak-to-valley of less than 5 nm typically. A 5 nm texture appears mirror-like to the untrained eye. Special polishing equipment is necessary to achieve circumferential texture this fine such as is described in Jones, et al., U.S. Pat. No. 5,490,809. The topography of the surface on which a thin film is deposited can have a significant effect on the way the film nucleates and grows and also upon its characteristics. So called circumferential texture on magnetic disks has been commonly used to influence the inplane magnetic anisotropy for a wide range of magnetic alloys. For longitudinal recording it is sometimes useful to have a higher coercivity (Hc) in the circumferential direction than in the radial direction. The ratio of the circumferential Hc to the radial Hc is called the orientation ratio (OR). For example, Kneller U.S. Pat. No. 4,287,225 states that he was able to obtain uniaxial magnetic anisotropy (i.e. OR>1) using circumferential texture with an amorphous SmCo alloy. Others have shown similar effects with body-centered cubic (bcc) alloys. Current disks typically use hexagonal close packed (hcp) cobalt alloys and most (but not all) circumferentially textured disks have an OR>1.
U.S. Pat. No. 6,567,236 to Doerner, et al., describes a preferred embodiment of a layer structure as: a pre-seed layer preferably of CrTi, a seed layer preferably of RuAl, an underlayer preferably of CrTi, a bottom ferromagnetic layer preferably of CoCr, an antiferromagnetic coupling/spacer layer preferably of Ru; and a top ferromagnetic structure including: a thin first sublayer of material preferably of CoCr, CoCrB or CoPtCrB, and a thicker second sublayer of material preferably of CoPtCrB with a lower moment than the first sublayer.